Cities and towns throughout the world depend on having clean potable water supplies. The dependence on clean water has increased as the population of the world has increased, especially as industrial use of rivers and lakes have become commonplace.
The explosion of world population, and corresponding increase in fresh water use, has, therefore, resulted in a need to maximize water usage. However, the ability to maximize fresh water use has been limited by, (1) increased pollution of the fresh water supplies due to higher industrial output throughout the world (a direct result of the increased population); and (2) increased knowledge and standards for what constitutes clean water, acceptable for use in farming, industry, and consumption. As a result, there is a current need to increase the efficiency in the use of water, i.e., conserve existing clean water supplies, increase the current capabilities used to remove pollutants from water supplies, and increase the effectiveness of existing and new technologies to effectively treat and reach new standards in water quality.
In order to facilitate an understanding of clean water concerns in relation to a pollutant, arsenic will be discussed. Arsenic, a soluble element that occurs naturally, has become of concern to the water supplies of many population centers throughout the world, and in particular, portions of the world where the element is found in high concentrations, e.g., Bangladesh, Northern Chile, etc. Of particular importance to these areas of high arsenic concentration, and to other lower arsenic concentration areas as well, is the fact that arsenic has been found to be a toxin and carcinogen and accumulates within tissues over a period of time.
The drinking water standard for arsenic, set in the 1940's, was originally 50 parts per billion (ppb). Over the last several decades, the Environmental Protection Agency (EPA) and academia have been studying the potential health effects of arsenic intake, and in particular have focused on the health effects of arsenic in and around the EPA set level of 50 ppb. For example, at arsenic levels of around 100 ppb there appear to be potential serious health effects on humans, such as increased potential of certain cancers and a weakened immune system. However, at arsenic levels closer to 50 ppb and lower, the studies show conflicting results as to arsenic's effects on health, suggesting that additional studies are needed to clarify what level of arsenic is appropriate for long term consumption in drinking water.
In the 1990's the EPA recommended that the arsenic limit in drinking water be lowered to 10 ppb. No action was taken on the EPA's proposal until days before the Clinton administration was scheduled to leave office, at which time President Clinton approved of arsenic levels being lowered from 50 ppb to 10 ppb. In addition, wide spread support for further lowering the standard to 5 ppb arsenic has gained acceptance within a number of environmental groups. There are a significant number of drinking water facilities that would violate an arsenic standard lower than the 50 ppb standard. In particular, over 3,500 drinking water facilities in at least 24 states would violate a 5 ppb arsenic standard, illustrating the need for utilizing some type of arsenic removal system in at least these facilities.
Currently, commercial scale removal of arsenic is accomplished using granulated ferric oxide and activated alumina, or to a lesser extent, by using ferric hydroxide. Although theoretically effective at arsenic removal, these techniques are costly, tending to run in the range of $1,200/ton for the activated alumina or for the ferric hydroxide, thereby making their use less attractive. Additionally, granular ferric hydroxide has proven to be friable, adding to the cost of using the compound, and activated alumina has proven to have a higher affinity for fluorine than arsenic, making high fluorine water sources unacceptable targets for the activated alumina technique. As such, there is a need in the industry for providing an arsenic removal system that overcomes these current deficiencies in arsenic removal, and has the ability to sufficiently treat water supplies and reach the proposed MCL for arsenic, whether it be 10 ppb or 5 ppb. Ideally these new arsenic removal techniques are cost effective and useful in high fluorine containing water supplies. Against this backdrop the present invention has been developed.